Falkenstein and Burg Nurings
Since my original visit to Falkenstein in late 1977, to my next visit which was in Sept of 2012, much has changed at the site. Restoration work has cleared away the extensive brush that had obscured sections of walls, while excavations had uncovered  the foundations and partial walls of other buildings within the castle grounds.

Moreover, excavations had uncovered the remains of Burg Nurings, a castle that predates Falkenstein.
Above, a view of part of the battlements that protected the main gate. Right, the main gate (to the left) and adjoining sections that served to protect that gate as seen from within. A turret (remains at center) protected the entrance.

Below, a view to the restored foundations of various buildings that were part of the Vorburg, or outer castle that protected the keep. Below right, a view within one of these restored sections. The walls seem authentic, but the floor surface is recent.
Right, a view into the Vorburg.  Thirty years ago this area was mostly obscured by debris and brush.

Below, a nice view of the keep from the Vorburg. Unfortunately, while more of the castle has been restored the keep is now closed for safety reasons. It was open in 1977.
Right, the remains of a typical tower castle from around 1100 AD. This castle was called Nurings (or Norings) for the Graf von Nurings family from the Mosel region. The castle originally dates from the 1000s, but the 15 meter stone tower, of which only a preserved foundation remains (photo), was built in the 1100s.

The tower, which had a roughly square wall about it, was extant into the 1400s, meaning that two castles occupied the Falkenstein site for around 150 years. It was ultimately abandoned and dismantled. As for the Nurings family, their line would die out around 1170, with their properties absorbed by other families like the Munzenberg and Falkenstein.

The site was so obscure until recently that Curt Tillmann placed a simple entry in his lexicon without any other data or precise location, only noting that it was "south" of Falkenstein. As it were, the sites are almost co-located. Excavations were done in 1997 and into the early 2000s.
Below... a view south towards Frankfurt/Main, its skyscrapers just visible above the mist.